This is not how you should register a receiver. You receiver stops working, because you construct it in onCreate, which means it will live as long as your app is alive. When the app gets destroyed, you also lose the the receiver.
If you register receiver inside an activity, you should always register it in onResume and deregister onPause, which will make it available while the activity is visible to the user. This is a use case when you want to have an active receiver while user interacts with an activity.
If you want a background receiver, you need to register it inside the AndroidManifest (with intent filter), add an IntentService and start it when you receive a broadcast in the receiver.
Here is a tutorial, you are interested in chapter 3.
If you need to be always on, start a foreground service. There is function in Service that lets you: startForeground. Then register your receiver when service is created and deregister when it’s destroyed. Foreground services are quite nasty though.